fixup! ci: add a simple cmake build test

Author: pbruenn

.gitlab-ci.yml

@@ -69,6 +69,8 @@ build-cmake:
   stage: build
   tags:
     - docker
+  before_script:
+    - apt-get update && apt-get --assume-yes install cmake
   script:
     - cmake -S . -B build
     - cmake --build build